Oshkosh Corporation JLG E400AJP Service And Maintenance Manual Download

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SECTION 7 - BASIC TROUBLESHOOTING, ELECTRICAL INFORMATION, & SCHEMATICS

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– JLG Lift –

7-21

Current Measurement

• Set up the meter for the expected current range

• Be sure to connect the meter leads to the correct

jacks for the current range you have selected

• If meter is not auto ranging, set it to the correct

range (See multi meter’s operation manual)

• Use firm contact with meter leads

7.4 CHECKING SWITCHES

Basic Check

The following check determines if the switch is functioning
properly, not the circuit in which the switch is placed. A
switch is functioning properly when there is continuity
between the correct terminals or contacts only when
selected.

1. De-energize the circuit.

2. Isolate the switch from the rest of the circuit if possi-

ble. If not possible, keep in mind it may affect read-
ings.

3. Access the terminals to the switch.

4. If the switch has two terminals:

a. Measure resistance across the terminals.

b. Change the switch position.
c. Measure resistance again with the leads in the

same positions. If the meter was reading short, it
should read an open. If the meter was reading
open it should read short.

5. If the switch has more than two terminals, consult

the schematic or switch diagram to determine what
terminals will be connected. The test is similar to
testing a switch with two terminals.

a. Place one meter lead on the common contact

and the other on a different contact in the same
circuit.

b. Cycle through all positions of the switch. The

meter should read short only when the switch
connects the two terminals and open otherwise.

c. If the switch has more than one common contact

repeat the process for that circuit.

Limit Switches

Limit switches are used to control movement or indicate
position. Mechanical limit switches are just like manually
operated switches except that the moving object operates
the switch. These switches can be tested the same way as
a standard switch by manually operating the sensing arm.

Another type of limit switch used by JLG is the inductive
proximity switch, also referred to as a "prox switch". Induc-
tive proximity switches are actuated only by ferrous metal
(metal that contains Iron, such as steel) near the switch.
They do not require contact, and must be energized to
actuate. These types of switches can be used to detect
boom or platform position, for example. These switches
have a sensing face where the switch can detect ferrous
metal close to it. To find the sensing face, take note how
the switch is mounted and how the mechanisms meet the
switch. Test this type of switch as follows:

1. Remove prox switch from its mount.

2. Reconnect harness if it was disconnected for step a,

and turn on machine.

3. Hold switch away from metal and observe switch

state in the control system diagnostics using the
Analyzer. See vehicle or control system documenta-
tion on how to do this.

4. Place sensing face of switch on the object to be

sensed by the switch. If that is not available, use a
piece of ferrous metal physically similar to it. The
switch state in the control system diagnostics
should change.

5. When reinstalling or replacing switch be sure to fol-

low mounting instructions and properly set the gap
between the switch and object sensed.

Figure 7-4. Current Measurement (DC)